Recently the N4CLA 145.47mhz. 2 meter repeater in Atlanta, Ga., had an issue with an FM Station's music showing up on the Repeaters Carrier. It was down in the background but clearly heard. The repeater is located on a mountain with many others and 2x50KW FM stations and 5 TV stations including 1 digital station. The FM Station antenna is just across the street about 100 feet away from the repeater antenna. The antenna and feedline couple lots of RF from the FM station into the repeater shack. The FM station upgraded to HD. The Salsa started (it's a station that plays salsa style music). After a couple of trips up to the site with no results accomplished, 3 of us went up there determined to fix it. After lots of bypassing this and that, we added a large RF choke on the output cable of the Micor PA. Repeater is GE RX and Exciter, PA is Motorola 100W Micor. The Salsa went away. We added a second for good measure and left. The Digital Modulation was being rectified in the Micor PA and added to our carrier. The choke stopped the common mode RF on the cable from getting into the PA. Our next step is to provide a 1/4 wave shunt on the transmission line where it enters the shack on both antenna cables.
Just another head scratcher to add to the Fix list. Steve W4CNG
